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Bits of Resolution!

Posted by Bromo33333 (A) on October 18, 2015 at 09:11:11

In Reply to: The 4 ways to decode digital posted by J. Phelan on October 13, 2015 at 14:11:32:

1. Commercial "Delta-Sigma" DAC chips - typically have under 20 bits of resolution. The absolute state of the art is 21bits. This translates to 120dB-126dB of dynamic range, so it isn't bad at all. The Burr-Brown you single out at 18bits is pretty run of the mill. Sounds good too.

2. Programmable discrete logic/DSP/FPGA/etc.: THat's a digital architecture that allows someone to "roll their own" when it comes to filtering. You still have to do a DAC step. And PSAudio is converting everything from PCM to DSD (like the NAD does, actually) and then filtering. I think the NAD usses the PWM signal to drive the output stage and does the filtering at the end. The PS Audio can't do that (patent violation) so filters and then uses an analog buffer/amp for the output. Each, of course, uses a different sample rate, but both ARE 1 bit signals at a really high rate of sampling. (Which is all DSD really is, for the record).

3. Ladder Networks: Problems with loss of linearity towards the LSB due to unavoidable error stack-up. TOTALDAC threw money at the problem, which is cool, but even they "only" get about 14 bits of resolution. (84dB dynamic range for those counting) - there is a lot more ot digital sound than dynamic range, but realize from a linearity and dynamic range point of view it's not as good as other methods. For the record, both Resolution Audio Cantata, and Audio Note UK use ladder networks, too. They sound pretty good as well. (Not for nothing, Ladder networks are great when you have 8-10 bits per word to decode). [TotalDAC uses a calculation to "prove" a dynamic range of the ladder network itself. Which is academically interesting, but not useful for an end user. They may simply be proving that they ask their customer to shell out $10k on a 14bit DAC that they could have built for a lot less.

4. Conversion from PCM to PWM/DSD: It is growing in popularity, but does require some digital noise shaping. But you are no longer "bit perfect" for those that care about that. But it allows for a simpler decoding.

PS Audio, NAD both use this though slightly different form each other. It requires all kinds of DSP gymnastic up front to have the simple DAC, so it isn't a free lunch. It hasn't reduced cost at all, and the performance gains aren't night and day (a good PCM DAC still sounds great compared to these implementations - as do these implementations to them). It makes a few things easier (you can directly feed switch mode amplification in some cases) but other things become harder (custom chipsets, or expensive DSP and all kinds of DSP expretise needed).

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"You are precisely as big as what you love and precisely as small as what you allow to annoy you." ~ R A Wilson

Edits: 10/18/15 10/18/15

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